Wind turbine generator, active damping method thereof, and windmill tower

ABSTRACT

A wind turbine generator, an active damping method thereof, and a windmill tower in which vibrations of the wind turbine generator itself or the windmill tower can be reduced at low cost are provided. The acceleration due to vibrations of a nacelle is detected with an accelerometer attached to the nacelle. In an active damping unit, a pitch angle of windmill blades for generating a thrust on the windmill blades so as to cancel out the vibrations of the nacelle is calculated on the basis of the acceleration, and the pitch angle is output as a blade-pitch-angle command δθ* for damping. On the other hand, in a pitch-angle control unit, a pitch angle of the windmill blades for controlling the output to be a predetermined value is calculated, and the pitch angle is output as a blade-pitch-angle command θ* for output control. The blade-pitch-angle command δθ* for damping is combined with the blade-pitch-angle command θ* for output control using a subtracter. The pitch angle of the windmill blades is controlled on the basis of the resulting blade-pitch-angle command after combining.

RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.12/727,356, filed Mar. 19, 2010, which is a divisional of U.S.application Ser. No. 10/590,328, filed Jun. 25, 2007, which is a U.S.National Stage of PCT/JP2004/16851, filed Nov. 12, 2004, and claimspriority from Japanese Application Number 2004-055515, filed Feb. 27,2004, the disclosures of which are hereby incorporated by referenceherein in their entirety.

TECHNICAL FIELD

The present invention relates to wind turbine generators, active dampingmethods thereof, and windmill towers in which vibrations induced byfluctuations of wind speed can be suppressed. In particular, the presentinvention relates to wind turbine generators, active damping methodsthereof, and windmill towers in which vibrations of the wind turbinegenerators themselves or the windmill towers can be reduced at low costand without increasing the weight of a nacelle.

BACKGROUND ART

Wind turbine generators generally have a structure in which heavyobjects such as blades, a gearbox, and a generator are provided at thetop of a cylindrical tower having a height of several tens of meters;therefore, vibrations induced by fluctuations of wind speed areextremely large. Such vibrations increase the fatigue loading ofstructural components, resulting in a decrease in the life of thewindmill tower.

Recently, the size of wind turbine generators has been increased. As thesize of the generators increases, the effect of vibrations induced byfluctuations of wind speed becomes more significant. Thus, reducing thevibrations in wind turbine generators or windmill towers is a criticaltechnical problem.

On the other hand, in tall structures such as high-rise buildings,active damping techniques are used in order to improve the livingconditions during strong winds. Various methods have been proposed, butmost of them involve driving a heavy object (mass) provided on the upperpart of the structure with an actuator such as a motor to absorb thevibrations of the structure itself; one example is an active mass damper(AMD).

However, when the active damping technique (AMD) used in high-risestructures and the like is directly applied to wind turbine generatorsor windmill powers without modification, the following problems occur.

First, in order to achieve a satisfactory damping effect, a considerablyheavy object (mass) is necessary. Furthermore, in order to drive thisconsiderably heavy object, an actuator having a large capacity must beprovided. Consequently, the weight of the nacelle significantlyincreases.

Secondly, since the weight of the nacelle disposed at the top of awindmill tower increases, the strength of the windmill tower supportingthe nacelle must be increased accordingly. This need to significantlyincrease the strength of the windmill tower and other componentsincreases the total cost of the wind turbine generator and the windmilltower.

Thirdly, an actuator for driving the heavy object (mass) is necessary.Accordingly, the number of parts for driving is increased, resulting inincreased maintenance costs.

To solve the above problems, for example, Japanese Unexamined PatentApplication Publication No. 2001-221145 (Patent Document 1) discloses atechnique in which vibrations of a windmill tower are suppressed byproviding a passive-active pitch-flap mechanism.

[Patent Document 1]

-   Japanese Unexamined Patent Application Publication No. 2001-221145

DISCLOSURE OF INVENTION

However, the invention described in Patent Document 1 ultimately employsa method of reducing vibrations of the windmill tower using a mechanicalmechanism. Therefore, this method is no different from the known AMDmethod, resulting in an increase in the weight of the nacelle.Furthermore, a plurality of structures are included, resulting inproblems such as an increase in the size of the nacelle and an increasein the cost.

The present invention has been made in order to solve the aboveproblems, and an object of the present invention is to provide windturbine generators, active damping methods thereof, and windmill towersin which vibrations can be reduced at low cost and without increasingthe weight of the nacelle.

In order to solve the above problems, the present invention provides thefollowing solutions.

The present invention provides a wind turbine generator including apitch-angle control mechanism for controlling a pitch angle of windmillblades on the basis of a blade-pitch-angle command, wherein the windturbine generator includes an accelerometer, attached to a nacelle, fordetecting the acceleration due to vibrations of the nacelle; and anactive damping unit for calculating a pitch angle of the windmill bladesfor generating a thrust on the windmill blades so as to cancel out thevibrations of the nacelle on the basis of the acceleration detected withthe accelerometer and for outputting a blade-pitch-angle command to thepitch-angle control mechanism.

According to the present invention, the acceleration due to vibrationsof the nacelle is detected with the accelerometer attached to thenacelle, a pitch angle of the windmill blades for generating a thrust onthe windmill blades so as to cancel out the vibrations of the nacelle iscalculated in the active damping unit on the basis of the acceleration,and the pitch angle is output as a blade-pitch-angle command to thepitch-angle control mechanism, thereby controlling the pitch angle ofthe windmill blades. In this case, the drag acting on the windmill bladeacts as a thrust in the front-rear direction of the nacelle, and themagnitude of the thrust varies depending on wind speed and the pitchangle of the windmill blade. Accordingly, when the pitch angle iscontrolled on the basis of a predetermined control rule, vibrations inthe front-rear direction of the nacelle can be controlled to someextent.

The present invention also provides a wind turbine generator including apitch-angle control mechanism for controlling a pitch angle of windmillblades on the basis of a blade-pitch-angle command, wherein the windturbine generator includes an accelerometer, attached to a nacelle, fordetecting the acceleration due to vibrations of the nacelle; an activedamping unit for calculating a pitch angle of the windmill blades forgenerating a thrust on the windmill blades so as to cancel out thevibrations of the nacelle on the basis of the acceleration detected withthe accelerometer and for outputting a blade-pitch-angle command fordamping; a pitch-angle control unit for calculating a pitch angle of thewindmill blades for controlling the output of the wind turbine generatorto be a predetermined value on the basis of wind speed, the rotationalspeed of a windmill rotor, or the output of the wind turbine generatorand for outputting a blade-pitch-angle command for output control; andan adder for supplying the pitch-angle control mechanism with ablade-pitch-angle command obtained by combining the blade-pitch-anglecommand for damping output from the active damping unit with theblade-pitch-angle command for output control output from the pitch-anglecontrol unit.

According to the present invention, the acceleration due to vibrationsof the nacelle is detected with the accelerometer attached to thenacelle. A pitch angle of the windmill blades for generating a thrust onthe windmill blades so as to cancel out the vibrations of the nacelle iscalculated in the active damping unit on the basis of the acceleration,and the pitch angle is output as a blade-pitch-angle command fordamping. On the other hand, a pitch angle of the windmill blades forcontrolling the output to be a predetermined value is calculated in thepitch-angle control unit, and the pitch angle is output as ablade-pitch-angle command for output control. The blade-pitch-anglecommand for damping is combined with the blade-pitch-angle command foroutput control by the adder. Thus, the pitch angle of the windmillblades is controlled on the basis of the resulting blade-pitch-anglecommand after combining.

Since the technique of pitch-angle control has been widely employed todate for the purpose of output control, the present invention can berealized by merely additionally mounting the accelerometer, the activedamping unit, and the adder on an existing wind turbine generator.Accordingly, the cost of installing and operating the active dampingcontrol can be markedly reduced, and thus vibrations of the wind turbinegenerator can be reduced at low cost. Furthermore, since the pitch-anglecontrol is performed by combining the blade-pitch-angle command fordamping with the blade-pitch-angle command for output control, outputcontrol and damping control can be achieved at the same time.

In the wind turbine generator of the present invention, the activedamping unit preferably includes a speed estimation unit for estimatinga speed from the acceleration detected with the accelerometer, and acontrol unit for calculating a pitch angle of the windmill blades forgenerating a thrust on the windmill blades so as to cancel out thevibrations of the nacelle on the basis of the speed output from thespeed estimation unit.

According to this invention, in the active damping unit, the speedestimation unit estimates a speed from the acceleration detected withthe accelerometer. The control unit then calculates a pitch angle of thewindmill blades for generating a thrust on the windmill blades so as tocancel out the vibrations of the nacelle on the basis of the estimatedspeed.

Since the active damping unit can be realized by a simple structureincluding the speed estimation unit and the control unit, vibrations ofthe wind turbine generator can be reduced at low cost.

In the wind turbine generator of the present invention, the speedestimation unit preferably integrates the acceleration detected with theaccelerometer to calculate the speed.

Since the speed estimation unit integrates the acceleration detectedwith the accelerometer to calculate the speed, noise in thehigh-frequency band can be removed. Thereby, the control unit in thesubsequent stage can perform stable and effective damping control.

In the wind turbine generator of the present invention, the control unitpreferably includes a phase-lead compensator for advancing the phase ofthe speed output from the speed estimation unit by a predeterminedamount, and preferably calculates the pitch angle on the basis of thespeed obtained after the phase-lead compensation.

Furthermore, the control unit preferably includes a phase-lagcompensator for delaying the phase of the speed output from thephase-lead compensator by a predetermined amount, and preferablycalculates the pitch angle on the basis of the speed obtained after thephase-lag compensation.

According to this invention, the pitch angle is calculated on the basisof the speed obtained after the phase-lag compensation. Since thephase-lag of the output of the accelerometer can be compensated for andnoise in the high-frequency band can be reduced, stable and effectivedamping control can be performed.

In the wind turbine generator of the present invention, the control unitpreferably includes any one of a proportional controller, aproportional-integral controller, a proportional-integral-derivativecontroller, a linear-quadratic regulator, and a linear-quadraticGaussian regulator to which the speed estimated by the speed estimationunit is input to calculate the pitch angle.

When the control unit has such a structure, stable and effective dampingcontrol can be performed.

In the wind turbine generator of the present invention, the activedamping unit preferably includes a limiter for limiting the pitch angleof the windmill blades or the angular speed of the pitch angle of thewindmill blades to a predetermined range.

According to this invention, the active damping unit, more specifically,the control unit provided in the active damping unit, includes a limiterfor limiting the pitch angle of the windmill blades or the angular speed(rate of change) of the pitch angle of the windmill blades to apredetermined range. Therefore, fatigue of the pitch-angle controlmechanism can be reduced, and problems due to errors in setting theparameters or the like can be prevented.

Furthermore, when the blade-pitch-angle command for damping is limitedto a much smaller range than the blade-pitch-angle command for outputcontrol, effects caused by interference of both command values can bedecreased or prevented.

The present invention provides an active damping method of a windturbine generator including a pitch-angle control mechanism forcontrolling a pitch angle of windmill blades on the basis of ablade-pitch-angle command, and an accelerometer, attached to a nacelle,for detecting the acceleration due to vibrations of the nacelle, theactive damping method including an active damping step of calculating apitch angle of the windmill blades for generating a thrust on thewindmill blades so as to cancel out the vibrations of the nacelle on thebasis of the acceleration detected with the accelerometer and outputtinga blade-pitch-angle command to the pitch-angle control mechanism.

According to the present invention, the accelerometer attached to thenacelle detects the acceleration due to vibrations of the nacelle, apitch angle of the windmill blades for generating a thrust on thewindmill blades so as to cancel out the vibrations of the nacelle iscalculated in the active damping step on the basis of the acceleration,and the pitch angle is output as a blade-pitch-angle command to thepitch-angle control mechanism, thereby controlling the pitch angle ofthe windmill blades. Thus, the control can be realized by theaccelerometer, hardware of the pitch-angle control mechanism, andsoftware of the active damping step. Therefore, the cost of installingand operating the active damping control can be markedly reduced, andvibrations of the wind turbine generator can be reduced at low cost.

The present invention provides an active damping method of a windturbine generator including a pitch-angle control mechanism forcontrolling a pitch angle of windmill blades on the basis of ablade-pitch-angle command, and an accelerometer, attached to a nacelle,for detecting the acceleration due to vibrations of the nacelle, theactive damping method including an active damping step of calculating apitch angle of the windmill blades for generating a thrust on thewindmill blades so as to cancel out the vibrations of the nacelle on thebasis of the acceleration detected with the accelerometer and outputtinga blade-pitch-angle command for damping; a pitch-angle control step ofcalculating a pitch angle of the windmill blades for controlling theoutput of the wind turbine generator to be a predetermined value on thebasis of wind speed, the rotational speed of a windmill rotor, or theoutput of the wind turbine generator and outputting a blade-pitch-anglecommand for output control; and an addition step of supplying thepitch-angle control mechanism with a blade-pitch-angle command obtainedby combining the blade-pitch-angle command for damping in the activedamping step with the blade-pitch-angle command for output control inthe pitch-angle control step.

According to this invention, an accelerometer attached to the nacelledetects the acceleration due to vibrations of the nacelle, and a pitchangle of the windmill blades for generating a thrust on the windmillblades so as to cancel out the vibrations of the nacelle is calculatedin the active damping step on the basis of the acceleration to outputthe pitch angle as a blade-pitch-angle command for damping. On the otherhand, a pitch angle of the windmill blades for controlling the output tobe a predetermined value is calculated in the pitch-angle control stepto output a blade-pitch-angle command for output control. Theblade-pitch-angle command for damping is combined with theblade-pitch-angle command for output control in the addition step, andthe pitch angle of the windmill blades is controlled on the basis of theresulting blade-pitch-angle command after combining. Since the techniqueof pitch-angle control has been widely employed to date for the purposeof output control, the present invention can be realized merely addingthe active damping step and the addition step to existing controlsoftware on a wind turbine generator.

Thus, since the control can be realized by mounting the accelerometerand adding the software, the cost of installing and operating the activedamping control can be markedly reduced, and vibrations of the windturbine generator can be reduced at low cost. Furthermore, since thepitch-angle control is performed by combining the blade-pitch-anglecommand for damping with the blade-pitch-angle command for outputcontrol, output control and damping control can be achieved at the sametime.

In the active damping method of a wind turbine generator of the presentinvention, the active damping step preferably includes a speedestimation step of estimating a speed from the acceleration detectedwith the accelerometer, and a control step of calculating a pitch angleof the windmill blades for generating a thrust on the windmill blades soas to cancel out the vibrations of the nacelle on the basis of the speedestimated in the speed estimation step.

According to this invention, in the active damping step, a speed isdetermined in the speed estimation step on the basis of the accelerationdetected with the accelerometer, and a pitch angle of the windmillblades for generating a thrust on the windmill blades so as to cancelout the vibrations of the nacelle is calculated in the control step onthe basis of the speed. Since the active damping step can be realized bya simple structure including the speed estimation step and the controlstep, vibrations of the wind turbine generator can be reduced at lowcost.

In the active damping method of a wind turbine generator of the presentinvention, the speed estimation step preferably integrates theacceleration detected with the accelerometer to calculate the speed.

Since noise in the high-frequency band can be removed by the speedestimation step, stable and effective damping control can be performedin the active damping step.

In the active damping method of a wind turbine generator of the presentinvention, the control step preferably includes a phase-leadcompensation step of advancing the phase of the speed output from thespeed estimation step by a predetermined amount and calculates the pitchangle on the basis of the speed obtained after the phase-leadcompensation.

In the active damping method of a wind turbine generator of the presentinvention, the control step preferably includes a phase-lag compensationstep of delaying the phase of the speed output from the phase-leadcompensation step by a predetermined amount and calculates the pitchangle on the basis of the speed obtained after the phase-lagcompensation.

According to this invention, the control step includes a phase-leadcompensation step of advancing the phase of the speed output from thespeed estimation step by a predetermined amount, the control stepincludes a phase-lag compensation step of delaying the phase of thespeed output from the phase-lead compensation step by a predeterminedamount, and the pitch angle is calculated on the basis of the speedobtained after the phase-lag compensation. Accordingly, since thephase-lag of the output of the accelerometer can be compensated for andnoise in the high-frequency band can be reduced, stable and effectivedamping control can be performed.

In the active damping method of a wind turbine generator of the presentinvention, the control step preferably includes a compensation step ofperforming any one of a proportional control, a proportional-integralcontrol, a proportional-integral-derivative control, a control using alinear-quadratic regulator, and a control using a linear-quadraticGaussian regulator for the speed estimated by the speed estimation stepand calculates the pitch angle on the basis of the speed obtained afterthe compensation.

Thereby, stable and effective damping control can be performed.

In the active damping method of a wind turbine generator of the presentinvention, the active damping step preferably includes a limiting stepof limiting the pitch angle of the windmill blades or the angular speedof the pitch angle of the windmill blades to a predetermined range.

According to this invention, fatigue of the pitch-angle controlmechanism can be reduced, and problems due to errors in setting theparameters or the like can be prevented. Furthermore, when theblade-pitch-angle command for damping is limited to a much smaller rangethan the blade-pitch-angle command for output control, effects caused byinterference of both command values can be decreased or prevented.

The wind turbine generator of the present invention can be suitably usedfor a windmill tower.

By applying the wind turbine generator of the present invention to awindmill tower, the cost of installing and operating the active dampingcontrol can be markedly reduced, and vibrations of the windmill towercan be reduced at low cost. Furthermore, unlike the known AMD method,since a heavy object (mass) and an actuator for the heavy object are notused, the weight of the nacelle does not increase and the strength ofthe windmill tower need not be increased. Thus, vibrations of thewindmill tower can be reduced at low cost.

According to the wind turbine generator of the present invention,vibrations can be suppressed by an accelerometer, an active dampingunit, and a pitch-angle control mechanism without using a heavy objectand an actuator for driving the heavy object, which are used in theknown AMD method. Consequently, the cost of installing and operating theactive damping control system can be markedly reduced, resulting in anadvantage that vibrations of the wind turbine generator can be reducedat low cost.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram showing the configuration of a wind turbinegenerator according to an embodiment of the present invention.

FIG. 2 is a view illustrating forces acting on a windmill blade.

FIG. 3 is a graph showing an example of the relationship between thethrust and the pitch angle for a change in wind speed.

FIG. 4( a) is a schematic view of a windmill tower, and FIG. 4( b) is aschematic diagram in the case where the windmill tower is modeled as amechanical vibration system.

FIG. 5 is a block diagram of an active-damping control system accordingto an embodiment of the present invention.

FIG. 6 includes block diagrams each showing an example of the structureof a control unit of an active damping unit.

FIG. 7 is a flow chart showing an example of the details of the controlof a limiter shown in FIG. 6.

FIG. 8 is a flow chart showing an example of the details of the controlof the limiter shown in FIG. 6.

FIG. 9 is a block diagram of a control system in the case where theactive-damping control system is installed in an output control system.

FIG. 10 is a graph showing the characteristic of output from a windmillgenerator versus wind speed.

FIG. 11 is a graph showing an example of the frequency characteristic ofthe vibration amplitude in a tower system in cases where the activedamping is performed and is not performed by the active damping unit.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of a wind turbine generator, an active damping methodthereof, and a windmill tower of the present invention will now bedescribed in detail with reference to the attached drawings.

FIG. 1 is a diagram showing the configuration of a wind turbinegenerator according to an embodiment of the present invention. In thefigure, the wind turbine generator of this embodiment includes amechanical part 10 of the wind turbine generator, an active damping unit20, a pitch-angle control unit 30, and a subtracter 40. First, theoutline of the components in the wind turbine generator of thisembodiment will be described.

The mechanical part 10 of the wind turbine generator includes a windmillrotor 11, windmill blades 12, a nacelle 13, and an anemometer 16 as maincomponents. The nacelle 13 includes a gearbox 14, a generator 15, and anaccelerometer 17.

In the mechanical part 10 of the wind turbine generator, a plurality ofwindmill blades 12 attached to the windmill rotor 11 receive wind powerenergy and are rotated together with the windmill rotor 11. The speed isincreased by the gearbox 14, and the generator 15 is then driven togenerate electricity. Thus, the wind power energy is converted toelectrical energy. In FIG. 1, the structure includes the gearbox 14, buta direct drive system that does not include the gearbox 14 may also beused.

The accelerometer 17, which is a feature of the wind turbine generatorof this embodiment, is disposed inside the nacelle 13 and at a positionclose to the central part of the tower. The accelerometer 17 detects theacceleration due to vibrations in the front-rear direction of thenacelle 13.

The pitch-angle control unit 30 calculates a pitch angle of the windmillblades 12 for controlling an output P of this wind turbine generator tobe a predetermined value on the basis of a wind speed v measured withthe anemometer 16, a rotational speed N of the windmill rotor 11, or theoutput P of the wind turbine generator, and outputs the pitch angle as ablade-pitch-angle command θ* for output control. This output control bycontrolling the pitch angle has been performed in the known art, and thepitch-angle control unit 30 of this embodiment is the same as that ofthe known art.

The active damping unit 20 calculates a pitch angle of the windmillblades 12 for generating a thrust on the windmill blades 12 so as tocancel out vibrations of the nacelle 13 on the basis of the accelerationdetected with the accelerometer 17, and outputs the pitch angle as ablade-pitch-angle command δθ* for damping.

The subtracter (adder) 40 combines the blade-pitch-angle command δθ* fordamping obtained from the active damping unit 20 with theblade-pitch-angle command θ* for output control obtained from thepitch-angle control unit 30 and provides the result to the pitch-anglecontrol mechanism as a blade-pitch-angle command. Here, the pitch-anglecontrol mechanism (not shown in the figure) controls the pitch angle ofthe windmill blades 12 on the basis of the blade-pitch-angle command,and the structure thereof and the like are the same as those of theknown art.

Next, the detailed structure of the active damping unit 20 and an activedamping method for reducing vibrations of the wind turbine generator andthe windmill tower using the active damping unit 20 will be described indetail.

First, the basic principles of the active damping method will now bedescribed with reference to FIGS. 2 and 3. FIG. 2 shows a cross-sectionof one of the windmill blades 12 (see FIG. 1) viewed from the leadingend of the windmill blade 12 toward the base thereof, and illustratesforces acting on the windmill blade 12. In the figure, the rotationdirection of the windmill blade is the direction from the right to theleft, and the vibration direction of the wind turbine generator or thewindmill tower is the vertical (x) direction. FIG. 3 is a graph showingan example of the relationship between the thrust and the pitch angle inthe case where the wind speed v is varied from 6 to 24 [m/s].

As shown in FIG. 2, during the windmill operation, a lift L and a drag Dact on the windmill blade. The drag D acts as a thrust in the front-reardirection of the nacelle 13 (see FIG. 1) of the windmill tower. As shownin FIG. 3, the magnitude of the thrust varies depending on the windspeed and the pitch angle. Accordingly, when the pitch angle iscontrolled on the basis of a control rule, by changing the thrust in thefront-rear direction of the nacelle 13 of the windmill tower, vibrationsin the front-rear direction of the nacelle 13 of the windmill tower canbe controlled to some extent. The present invention focuses on thispoint, and the control rule of the pitch angle will be described below.

FIG. 4( a) is a schematic view of the windmill tower, and FIG. 4( b) isa schematic diagram in the case where the windmill tower is modeled as amechanical vibration system. Specifically, FIG. 4( a) schematicallyshows that the accelerometer 17 is provided in the nacelle 13 of thewindmill tower to detect acceleration (d²x/dt²) for a displacement x. Asshown in FIG. 4( b), the windmill tower can be modeled using an objectwith a mass m, a spring with a stiffness k, and a dashpot with a viscousresistance c.

In this mechanical vibration system, when the displacement shifted fromthe equilibrium state is defined as x, the equation for the vibrationsof the object is represented by equation (1):

m{umlaut over (x)}+c{dot over (x)}+kx=f+Δf  (1)

In the equation, f+Δf represents the force acting on the object, and Δfrepresents an additional force exerted by the pitch control operation ofthe active damping unit 20.

Equation (1) is transformed into equation (2):

$\begin{matrix}{{\overset{¨}{x} + {\frac{c}{m}\overset{.}{x}}\; + {\frac{k}{m}x}} = {\frac{1}{m}\left( {f + {\Delta \; f}} \right)}} & (2)\end{matrix}$

Here, a natural frequency ωn of the system and a damping factor ζ arerepresented as follows, and thus equation (2) can be rewritten asequation (5).

$\begin{matrix}{{\omega \; n} = \left( {k/m} \right)^{\frac{1}{2}}} & (3) \\{\zeta = {{c/2}({mk})^{\frac{1}{2}}}} & (4) \\{{\overset{¨}{x} + {2{\zeta\omega}_{n}\overset{.}{x}} + {\omega_{n}^{2}x}} = {\frac{1}{m}\left( {f + {\Delta \; f}} \right)}} & (5)\end{matrix}$

Furthermore, equation (5) is subjected to a Laplace transformation toderive equation (6):

s ² X(s)+2ζωnsX(s)+ωn ² X(s)=(1/m)F(s)  (6)

From equation (6), a transfer function G(s) of the system is representedby equation (7):

G(s)=X(s)/F(s)=(1/m)/(s ²+2ζωns+ωn ²)  (7)

In the second-order frequency response characteristics as in equation(7), referring to equations (3) and (4), the natural frequency ωn of thesystem can be changed by changing the mass m and the stiffness k;however, regarding the damping factor ζ, the effect of a change in theviscous resistance c is larger than the effect of changes in the mass mand the stiffness k.

On the other hand, in equation (1), the additional force Δf is set, forexample, as follows.

Δf=−Dp{dot over (x)}  (8)

In this case, equation (1) can be rewritten as equation (9).

m{umlaut over (x)}+(C+Dp){dot over (x)}+kx=f  (9)

That is, by setting the additional force Δf exerted by the pitch controloperation of the active damping unit 20 as represented by equation (8),the first-order term of equation (9) is increased by +Dp, and thus thedamping factor ζ can be changed to a larger value. Consequently, dampingof the vibrations can be performed more rapidly, and in the frequencyresponse characteristics, a peak value of the gain of the naturalfrequency ωn can be suppressed more to suppress the vibration amplitude.

Next, the specific structure and operation of the active damping controlwill be described in detail on the basis of the above-described basicprinciples of the active damping method. FIG. 5 is a block diagram of anactive-damping control system according to this embodiment.

In FIG. 5, reference numeral 51 indicates a pitch actuator that drivesthe windmill blades 12 on the basis of the blade-pitch-angle commandoutput from the subtracter 40 to control the pitch angle. The pitchactuator 51 is specifically realized by a hydraulic cylinder, anelectric motor, or the like. Here, from the standpoint of the mechanicalvibration system, the pitch actuator 51 is modeled by a first-order lagsystem.

Reference numeral 52 indicates a blade system that calculates the thrustacting on the windmill blades during the windmill operation. As shown inFIG. 2, since the thrust in the front-rear direction of the nacelle 13of the windmill tower is the sum of the front-rear directionalcomponents of the lift L and the drag D, an adder 54 adds thesecomponents and outputs the result. Regarding the thrust due to the dragD, the pitch angle of the windmill blade 12 and the thrust havecharacteristics shown in FIG. 3. Accordingly, the thrust is consideredto be in inverse proportion to the pitch angle, and is determined withan amplifier 53 having a gain of Kb based on a gradient obtained bylinear approximation of the above relationship.

Reference numeral 55 indicates a tower system in which the windmilltower is modeled as a mechanical vibration system. The transfer functionis determined by equation (7), but in the active-damping control system,the acceleration (d²x/dt²) is detected with the accelerometer 17 and theresult is fed back. Therefore, the modeling is performed using atransfer function obtained by multiplying equation (7) by s². This modelis a model of only a first-order vibration mode.

A known wind turbine generator also has a structure including theabove-described pitch actuator 51, the blade system 52, and the towersystem 55. In this embodiment, the accelerometer 17, the active dampingunit 20, and the subtracter 40 are added to these components to form afeedback loop. The accelerometer 17 detects acceleration, which is theoutput of the tower system 55. The active damping unit 20 generates theblade-pitch-angle command δθ* for damping used for changing the thrustin the front-rear direction of the nacelle 13 of the windmill tower. Thesubtracter 40 performs a calculation of δθ*−θ* so as to combine theblade-pitch-angle command δθ* for damping obtained from the activedamping unit 20 with the blade-pitch-angle command θ* for output controloutput from the pitch-angle control unit 30.

The accelerometer 17 is modeled by a first-order lag system because theoutput thereof includes a phase lag. In the active damping unit 20, asset in equation (8), a value obtained by multiplying the speed (dx/dt)by Dp is defined as the additional force exerted by the pitch controloperation of the active damping unit 20. Therefore, the active dampingunit 20 includes an integrator 21 that integrates the acceleration todetermine the speed, and a control unit 22 having a transfer functionGc(s).

Specifically, the acceleration (first-order vibration mode) in thefront-rear direction of the nacelle 13 is measured with theaccelerometer 17 provided inside the nacelle 13, the measuredacceleration is input to the active damping unit 20, and the speed inthe front-rear direction of the nacelle 13 is calculated by anintegration operation by the integrator 21. In the control unit 22 ofthe active damping unit 20, the blade-pitch-angle command δθ* fordamping used for obtaining the damping effect is calculated on the basisof the calculated speed. The blade-pitch-angle command δθ* for dampingdetermined in the active damping unit 20 is combined, by the subtracter40, with the blade-pitch-angle command θ* for output control determinedin the pitch-angle control unit 30 (see FIG. 1). The pitch actuator 51drives the windmill blades 12 on the basis of the combinedblade-pitch-angle command to control the pitch angle. This pitch-anglecontrol controls the output of the wind turbine generator. In addition,a thrust according to the pitch angle acts so as to suppress vibrationsin the front-rear direction of the nacelle 13 of the windmill tower.Thus, the thrust allows the vibrations to be rapidly damped.

Thus, in this embodiment, by combining the blade-pitch-angle command δθ*for damping with the blade-pitch-angle command θ* for output control,output control and damping control can be achieved at the same time. Theintegrator 21, which calculates the speed, not only performs theintegration operation but also has a frequency characteristic thatrelatively suppresses a high-frequency band and emphasizes alow-frequency band. Accordingly, the integrator 21 also has a functionof cutting noise in the high-frequency band.

The structure of the integrator is not limited to the complete integral(1/s). Alternatively, the integrator may be a filter (for example, afirst-order lag element) having the same function as that of the above,an appropriate state estimator (a full-order or minimal-order observer,or a Kalman filter), or the like.

Next, the specific structure and operation of the control unit 22 of theactive damping unit 20 will now be described with reference to FIGS. 6(a) and 6(b). FIGS. 6( a) and 6(b) are block diagrams each showing anexample of the structure of the control unit 22 of the active dampingunit 20.

In FIG. 6( a), a control unit 22 a includes a phase-lead compensator 62,a phase-lag compensator 63, as amplifier 64, and a limiter 65.

As described above, since the output of the accelerometer 17 includes aphase lag, the phase-lead compensator 62 adjusts the phase. As shown inthe figure, the phase-lead compensator 62 has a transfer function of aphase-lead system represented by (1+sαT1)/(1+sT1) (wherein α<1).

When the output passes through the phase-lead compensator 62, noise inthe high-frequency band is amplified. Therefore, the phase-lagcompensator 63 is added as a countermeasure, thereby relativelysuppressing the high-frequency band and emphasizing the low-frequencyband. As shown in the figure, the phase-lag compensator 63 has atransfer function of a phase-lag system represented by (1+sαT2)/(1+sT2)(wherein α>1). Thus, the control unit 22 of the active damping unit 20includes two types of filter, i.e., the phase-lead compensator 62 andthe phase-lag compensator 63, thereby compensating for the phase-lag ofthe output of the accelerometer 17 and reducing noise in thehigh-frequency band. Therefore, stable and effective damping control canbe performed.

In addition, according to equation (8), the amplifier 64 is configuredto have a transfer function of a gain Dp. In this case, the gain Dp ispreferably set on the basis of the result of a simulation, anexperiment, or the like.

The structure of the control unit 22 (see FIG. 5) is not limited to theabove-described phase compensators. Alternatively, the control unit 22can be realized using, for example, a proportional controller, aproportional-integral controller, a proportional-integral-derivativecontroller, a linear-quadratic regulator (LQ regulator), or alinear-quadratic Gaussian regulator (LQG regulator).

When the pitch-angle control by the blade-pitch-angle command δθ* fordamping is performed too frequently, the pitch-angle control mechanismis excessively moved, resulting in fatigue. Therefore, a limit (forexample, ±1[deg]) is preferably provided for the blade-pitch-anglecommand δθ* for damping by the limiter 65 (see FIGS. 6( a) and 6(b)),thereby reducing fatigue of the pitch-angle control mechanism.

Specifically, when the output (hereinafter referred to as “pitch-anglecommand”) of the amplifier 64 shown in FIG. 6 is smaller than apredetermined minimum pitch-angle (“YES” in step SA1 in FIG. 7), theminimum pitch-angle or a predetermined pitch-angle larger than theminimum pitch-angle is output as the final blade-pitch-angle command δθ*for damping (step SA2 in FIG. 7). On the other hand, when thepitch-angle command is equal to or larger than the minimum pitch-angle(“NO” in step SA1 in FIG. 7), it is determined whether or not thepitch-angle command is larger than a predetermined maximum pitch-angle(step SA3 in FIG. 7).

As a result, when the pitch-angle command is larger than the maximumpitch-angle (“YES” in step SA3 in FIG. 7), the maximum pitch-angle or apredetermined pitch-angle smaller than the maximum pitch-angle is outputas the final blade-pitch-angle command δθ* for damping (step SA4 in FIG.7). On the other hand, when the pitch-angle command is equal to orsmaller than the maximum pitch-angle (“NO” in step SA3 in FIG. 7), thepitch-angle is output as the final blade-pitch-angle command δθ* fordamping (step SA5 in FIG. 7).

As described above, instead of limiting the output of the amplifier 64itself (see FIGS. 6( a) and 6(b)), the rate of change of this output,that is, the angular speed of the pitch angle, may be limited to acertain range (for example, ±0.6 [deg/sec]).

Specifically, as shown in FIG. 8, a rate of change is first calculatedon the basis of the previous value (hereinafter referred to as “previousvalue of pitch-angle command”) and a current value (hereinafter referredto as “current value of pitch-angle command”) of the output of theamplifier 64 (see FIG. 6) (step SB1). Subsequently, it is determinedwhether or not the rate of change is smaller than a predeterminedminimum rate of change (step SB2). As a result, when the rate of changeis smaller than the predetermined minimum rate of change (“YES” in stepSB2), a value calculated by adding the minimum rate of change to theprevious value of pitch-angle command is output as the finalblade-pitch-angle command δθ* for damping (step SB3).

On the other hand, when the rate of change is equal to or larger thanthe minimum rate of change (“NO” in step SB2), it is determined whetheror not the rate of change is larger than a predetermined maximum rate ofchange (step SB4). As a result, when the rate of change is larger thanthe maximum rate of change (“YES” in step SB4), a value calculated byadding the maximum rate of change to the previous value of pitch-anglecommand is output as the final blade-pitch-angle command δθ* for damping(step SB5). On the other hand, when the rate of change is equal to orsmaller than the maximum rate of change (“NO” in step SB4), the currentvalue of pitch-angle command is output as the final blade-pitch-anglecommand δθ* for damping (step SB6).

As described above, limiting the blade-pitch-angle command δθ* fordamping or the rate of change of the pitch-angle command δθ* can preventa problem where, for example, vibrations of the windmill tower areinstead increased because of errors in setting the parameters of thevibration control system or the like.

Furthermore, since the blade-pitch-angle command δθ* for damping islimited to a much smaller range than the blade-pitch-angle command θ*for output control, effects caused by interference of both commandvalues can be decreased or prevented.

In a control unit 22 b shown in FIG. 6( b), a second-order oscillatorycompensator 61 is added to the previous stage of the phase-leadcompensator 62 of the control unit 22 a to realize more precise control.

In the above description, the active damping unit 20 is composed ofhardware and outputs the blade-pitch-angle command δθ* for damping.Alternatively, each component may be composed of a subprogram that issequentially executed. In this case, the integrator 20 is replaced withan integration step (speed estimation step) and the control unit 22 isreplaced with a control step. Components in the control unit 22 are alsoreplaced with a phase-lead compensation step, a phase-lag compensationstep, a limiting step, and the like. These steps forms a subprogramexecuted in a central processing unit (CPU), a micro processing unit(MPU), or a digital signal processor (DSP) in a controller.

Next, the output control using the pitch-angle control unit 30 (seeFIG. 1) will be briefly described with reference to FIG. 9, which showsa block diagram of a control system in the case where theabove-described active-damping control system using the active dampingunit 20 is installed in an output control system, realized in a knownwind turbine generator, that uses the pitch-angle control unit 30.

In FIG. 9, the pitch-angle control unit includes subtracters 31 and 32,a wind-speed control unit 33, a rotational-speed control unit 34, anoutput control unit 35, and a selecting unit 36.

The wind-speed control unit 33 sets a blade-pitch-angle command θ_(v) onthe basis of a wind speed v [m/s] measured with the anemometer 16 andoutputs the command. The rotational-speed control unit 34 sets ablade-pitch-angle command θ_(N) so as to provide a predeterminedrotational speed (target value) N* on the basis of a rotational speed N[rpm] of the windmill rotor 11 and outputs the command. Furthermore, theoutput control unit 35 sets a blade-pitch-angle command θ_(P) so as toprovide a predetermined output (target value) P* on the basis of anoutput P [kW] of the wind turbine generator and outputs the command.

In the selecting unit 36, among the blade-pitch-angle commands θ_(v),θ_(N), and θ_(P) determined in the wind-speed control unit 33, therotational-speed control unit 34, and the output control unit 35,respectively, the minimum value is selected (minimum selection), thatis, a blade-pitch-angle command that produces the lowest output isselected, and is output as a blade-pitch-angle command θ* for outputcontrol. In general, characteristics between the output P [kW] of thewindmill generator and wind speed v [m/s] are illustrated as shown inFIG. 10. Control is performed on the basis of the wind speed v [m/s]until a rated output and a rated wind speed are achieved. After reachingthe rated output and the rated wind speed, control is performed on thebasis of the rotational speed N [rpm] of the windmill rotor 11 or theoutput P [kW] of the wind turbine generator.

The control range of the pitch angle by the pitch-angle control unit 30is large and ranges from a fine pitch (which is about −20 [deg] and atwhich the rotational speed is high) to a feathering pitch (which isabout −104 [deg] and at which the rotational speed is low).

Next, the advantage of the wind turbine generator and the active dampingmethod thereof according to this embodiment will be described withreference to example results of a simulation experiment. FIG. 11 shows afrequency characteristic of the vibration amplitude in the tower system55 (see FIG. 5) in cases where the active damping is performed and isnot performed by the active damping unit 20 (see FIG. 1). The figureshows that the vibration amplitude is substantially suppressed near thenatural frequency of the tower system 55. Since the natural frequency ofthe tower system 55 is known in advance, more appropriate vibrationcontrol can be realized by setting parameters of the control system inaccordance with the natural frequency.

As described above, in the wind turbine generator or the active dampingmethod thereof according to this embodiment, as shown in FIG. 1, theacceleration due to vibrations of the nacelle 13 is detected with theaccelerometer 17 attached to the nacelle 13, a pitch angle of thewindmill blades 12 for generating a thrust on the windmill blades 12 soas to cancel out the vibrations of the nacelle 13 is calculated in theactive damping unit 20 (active damping step) on the basis of theacceleration, and the pitch angle is output as a blade-pitch-anglecommand δθ* for damping. On the other hand, a pitch angle of thewindmill blades 12 for controlling the output to be a predeterminedvalue is calculated in the pitch-angle control unit 30 (pitch-anglecontrol step), and the pitch angle is output as a blade-pitch-anglecommand θ* for output control. Subsequently, the blade-pitch-anglecommand δθ* for damping is combined with the blade-pitch-angle commandθ* for output control using the subtracter 40 (addition step), and thepitch angle of the windmill blades is controlled on the basis of theresulting blade-pitch-angle command after combining.

Since the technique of pitch-angle control has been widely employed todate for the purpose of output control, this embodiment can be realizedby merely additionally mounting the accelerometer 17, the active dampingunit 20 (active damping step), and the subtracter 40 (addition step) onan existing wind turbine generator. Since the mounting can be easilyperformed, the cost of installing and operating the active dampingcontrol can be markedly reduced, and thus vibrations of the wind turbinegenerator can be reduced at low cost. Furthermore, since the pitch-anglecontrol is performed by combining the blade-pitch-angle command δθ* fordamping with the blade-pitch-angle command θ* for output control, outputcontrol and damping control can be achieved at the same time.

In the wind turbine generator of this embodiment or the active dampingmethod thereof, as shown in FIG. 1, in the active damping unit 20(active damping step), the acceleration detected by the accelerometer isintegrated with the integrator 21 (integration step) to determine thespeed, and a pitch angle of the windmill blades for generating a thruston the windmill blades so as to cancel out vibrations of the nacelle iscalculated by the control unit 22 (control step) on the basis of thespeed. Thus, according to the present invention, since the activedamping unit 20 (active damping step) can be realized using a simplestructure, i.e., the integrator 21 (integration step) and the controlunit 22 (control step), vibrations of the wind turbine generator can bereduced at low cost. Furthermore, since noise in the high-frequency bandcan be removed through the integrator 21 (integration step), stable andeffective damping control can be performed.

According to the wind turbine generator of this embodiment or the activedamping method thereof, as shown in FIGS. 1, 6(a), and 6(b), the controlunit 22 (control step) includes the phase-lead compensator 62(phase-lead compensation step) that advances the phase of the speedoutput from the integrator 21 (integration step) by a predeterminedamount and the phase-lag compensator 63 (phase-lag compensation step)that delays the phase of the speed output from the phase-leadcompensator 62 (phase-lead compensation step) by a predetermined amount,and calculates a pitch angle on the basis of the speed obtained afterthe phase-lag compensation. Thereby, the phase-lag of the output of theaccelerometer can be compensated for and noise in the high-frequencyband can be reduced, and thus stable and effective damping control canbe performed.

According to the wind turbine generator of this embodiment or the activedamping method thereof, as shown in FIGS. 6( a) and 6(b), the controlunit 22 (control step) includes the limiter 65 (limiting step) thatlimits the calculated pitch angle to a predetermined range. Therefore,fatigue of the pitch-angle control mechanism can be reduced, andproblems due to errors in setting the parameters or the like can beprevented.

Furthermore, when the blade-pitch-angle command δθ* for damping islimited to a much smaller range than the blade-pitch-angle command θ*for output control, effects caused by interference of both commandvalues can be reduced or prevented.

The embodiments of the present invention have been described in detailwith reference to the drawings. However, the specific structures are notlimited to the embodiments, and also include design changes that do notdepart from the essence of the present invention.

In the above description of the embodiments, the wind turbine generatorand the active damping method thereof have been described in detail. Thewind turbine generator of the embodiments and the active damping methodthereof can be directly applied to a windmill tower withoutmodification. In this case, in addition to the above-describedadvantages, the following advantages are also provided. Namely, unlikethe known AMD method, since a heavy object (mass) and an actuator forthe heavy object are not used, the weight of the nacelle 13 does notincrease and the strength of the windmill tower itself need not beincreased. Thus, the vibrations of the windmill tower can be reduced atlow cost.

In the embodiments, the output control is performed by the pitch-anglecontrol. However, the present invention can also be applied to a windturbine generator or a windmill tower that employs other outputcontrols. In this case, however, a pitch-angle control mechanism thatcontrols the pitch angle of the windmill blades 12 must be added.

Furthermore, in the actual operation, from the standpoint of increasingreliability and safety, the following structure or the method can alsobe employed.

In an example of the method, two accelerometers constantly operateinside the nacelle 13 for fail-safe operation, and only the detectionresult obtained from one of the accelerometers is used for the activedamping control. If either of the accelerometers breaks down, the activedamping control is automatically stopped.

When set values of parameters (mainly a feedback gain Gc(s)) of thedamping control system are not appropriate, for example, when the signis inverted or a high gain exceeding the tolerance limit is set, thedamping control system becomes unstable, resulting in an increase invibrations of the windmill tower (nacelle 13). In an example of themethod, such a state is automatically detected (with the accelerometer17 or the like) to automatically stop the active damping control.

1. A wind turbine generator including a pitch-angle control mechanismfor controlling a pitch angle of windmill blades on the basis of ablade-pitch-angle command, the wind turbine generator comprising: anaccelerometer, attached to a nacelle, for detecting the acceleration dueto vibrations of the nacelle; and an active damping unit for calculatinga pitch angle of the windmill blades for generating a thrust on thewindmill blades so as to cancel out the vibrations of the nacelle on thebasis of the acceleration detected with the accelerometer and foroutputting a blade-pitch-angle command to the pitch-angle controlmechanism.
 2. The wind turbine generator according to claim 1, whereinthe active damping unit includes a speed estimation unit for estimatinga speed from the acceleration detected with the accelerometer, and acontrol unit for calculating a pitch angle of the windmill blades forgenerating a thrust on the windmill blades so as to cancel out thevibrations of the nacelle on the basis of the speed output from thespeed estimation unit.
 3. The wind turbine generator according to claim3, wherein the speed estimation unit integrates the accelerationdetected with the accelerometer to calculate the speed.
 4. The windturbine generator according to claim 3, wherein the control unitincludes a phase-lead compensator for advancing the phase of the speedoutput from the speed estimation unit by a predetermined amount, andcalculates the pitch angle on the basis of the speed obtained after thephase-lead compensation.
 5. The wind turbine generator according toclaim 5, wherein the control unit includes a phase-lag compensator fordelaying the phase of the speed output from the phase-lead compensatorby a predetermined amount, and calculates the pitch angle on the basisof the speed obtained after the phase-lag compensation.
 6. The windturbine generator according to claim 3, wherein the control unitincludes any one of a proportional controller, a proportional-integralcontroller, a proportional-integral-derivative controller, alinear-quadratic regulator, and a linear-quadratic Gaussian regulator towhich the speed estimated by the speed estimation unit is input tocalculate the pitch angle.
 7. The wind turbine generator according toclaim 1, wherein the active damping unit includes a limiter for limitingthe pitch angle of the windmill blades or the angular speed of the pitchangle of the windmill blades to a predetermined range.
 8. An activedamping method of a wind turbine generator including a pitch-anglecontrol mechanism for controlling a pitch angle of windmill blades onthe basis of a blade-pitch-angle command, and an accelerometer, attachedto a nacelle, for detecting the acceleration due to vibrations of thenacelle, the active damping method comprising: an active damping step ofcalculating a pitch angle of the windmill blades for generating a thruston the windmill blades so as to cancel out the vibrations of the nacelleon the basis of the acceleration detected with the accelerometer andoutputting a blade-pitch-angle command to the pitch-angle controlmechanism.
 9. An active damping method of a wind turbine generatorincluding a pitch-angle control mechanism for controlling a pitch angleof windmill blades on the basis of a blade-pitch-angle command, and anaccelerometer, attached to a nacelle, for detecting the acceleration dueto vibrations of the nacelle, the active damping method comprising: anactive damping step of calculating a pitch angle of the windmill bladesfor generating a thrust on the windmill blades so as to cancel out thevibrations of the nacelle on the basis of the acceleration detected withthe accelerometer and outputting a blade-pitch-angle command fordamping; a pitch-angle control step of calculating a pitch angle of thewindmill blades for controlling the output of the wind turbine generatorto be a predetermined value on the basis of wind speed, the rotationalspeed of a windmill rotor, or the output of the wind turbine generatorand outputting a blade-pitch-angle command for output control; and anaddition step of supplying the pitch-angle control mechanism with ablade-pitch-angle command obtained by combining the blade-pitch-anglecommand for damping in the active damping step with theblade-pitch-angle command for output control in the pitch-angle controlstep.
 10. The active damping method of a wind turbine generatoraccording to claim 9, wherein the active damping step includes a speedestimation step of estimating a speed from the acceleration detectedwith the accelerometer, and a control step of calculating a pitch angleof the windmill blades for generating a thrust on the windmill blades soas to cancel out the vibrations of the nacelle on the basis of the speedestimated in the speed estimation step.
 11. The active damping methodaccording to claim 11, wherein the speed estimation step integrates theacceleration detected with the accelerometer to calculate the speed. 12.The active damping method of a wind turbine generator according to claim11, wherein the control step includes a phase-lead compensation step ofadvancing the phase of the speed estimated by the speed estimation stepby a predetermined amount and calculates the pitch angle on the basis ofthe speed obtained after the phase-lead compensation.